In this Letter, silver (Ag) hierarchical nanostructures grown on black silicon (BS) are used as the catalyst and a surface-enhanced Raman scattering (SERS) detector integrated in a microfluid. The BS is fabricated via femtosecond laser ablation in an atmosphere of sulfur hexafluoride, and then hydrogenated with hydrofluoric acid. As formed, the BS substrate directly acts as a reducing template to grow silver hierarchical nano-structures. Particularly, Ag-BS composite micro/nano-structures can be in-situ constructed in silicon-based microchannels. These structures simultaneously serve as integrated catalytic reactors and a SERS substrate for sensing. The sensitivity is tested to be as low as 10 8 mol/L using Rhodamine 6G.